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8299444: java.util.Set.copyOf allocates needlessly for empty input collections

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Reviewed-by: rriggs, shade, smarks
This commit is contained in:
Viktor Klang 2023-01-26 18:15:56 +00:00 committed by Stuart Marks
parent d98a323a8b
commit a2a7703370
3 changed files with 10 additions and 4 deletions
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8
src/java.base/share/classes/java/util/ImmutableCollections.java
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@ -1,5 +1,5 @@
/* /*
* Copyright (c) 2016, 2021, Oracle and/or its affiliates. All rights reserved. * Copyright (c) 2016, 2023, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
* *
* This code is free software; you can redistribute it and/or modify it * This code is free software; you can redistribute it and/or modify it
@ -166,10 +166,12 @@ class ImmutableCollections {
*/ */
@SuppressWarnings("unchecked") @SuppressWarnings("unchecked")
static <E> List<E> listCopy(Collection<? extends E> coll) { static <E> List<E> listCopy(Collection<? extends E> coll) {
if (coll instanceof List12 || (coll instanceof ListN && ! ((ListN<?>)coll).allowNulls)) { if (coll instanceof List12 || (coll instanceof ListN<?> c && !c.allowNulls)) {
return (List<E>)coll; return (List<E>)coll;
} else if (coll.isEmpty()) { // implicit nullcheck of coll
return List.of();
} else { } else {
return (List<E>)List.of(coll.toArray()); // implicit nullcheck of coll return (List<E>)List.of(coll.toArray());
} }
} }

2
src/java.base/share/classes/java/util/Map.java
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@ -1738,6 +1738,8 @@ public interface Map<K, V> {
static <K, V> Map<K, V> copyOf(Map<? extends K, ? extends V> map) { static <K, V> Map<K, V> copyOf(Map<? extends K, ? extends V> map) {
if (map instanceof ImmutableCollections.AbstractImmutableMap) { if (map instanceof ImmutableCollections.AbstractImmutableMap) {
return (Map<K,V>)map; return (Map<K,V>)map;
} else if (map.isEmpty()) { // Implicit nullcheck of map
return Map.of();
} else { } else {
return (Map<K,V>)Map.ofEntries(map.entrySet().toArray(new Entry[0])); return (Map<K,V>)Map.ofEntries(map.entrySet().toArray(new Entry[0]));
} }

4
src/java.base/share/classes/java/util/Set.java
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@ -1,5 +1,5 @@
/* /*
* Copyright (c) 1997, 2020, Oracle and/or its affiliates. All rights reserved. * Copyright (c) 1997, 2023, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
* *
* This code is free software; you can redistribute it and/or modify it * This code is free software; you can redistribute it and/or modify it
@ -728,6 +728,8 @@ public interface Set<E> extends Collection<E> {
static <E> Set<E> copyOf(Collection<? extends E> coll) { static <E> Set<E> copyOf(Collection<? extends E> coll) {
if (coll instanceof ImmutableCollections.AbstractImmutableSet) { if (coll instanceof ImmutableCollections.AbstractImmutableSet) {
return (Set<E>)coll; return (Set<E>)coll;
} else if (coll.isEmpty()) { // Implicit nullcheck of coll
return Set.of();
} else { } else {
return (Set<E>)Set.of(new HashSet<>(coll).toArray()); return (Set<E>)Set.of(new HashSet<>(coll).toArray());
} }